The present invention relates in a broad aspect to a device and a method for adjusting the pitch of a wind turbine and for stopping the rotation of the blades of a wind turbine.
In one aspect, the present invention relates to a method of adjusting the angular position of at least one blade of a wind turbine, the said wind turbine comprising a bevel gear and a motor for the rotation of a drive wheel of the bevel gear and drive pinions of the bevel gear for turning at least one blade at an angle, this at least one blade being turned at an angle by the drive pinions, the said drive pinions being rotated by the drive wheel, and the drive wheel being rotated by the motor relative to the main shaft. The invention also relates to a mechanism for controlling the pitch of at least one blade of a wind turbine relative to a wind direction parallel to a longitudinal main shaft of the wind turbine, the said mechanism comprising a motor for rotating drive wheels in the bevel gear around a longitudinal blade shaft via drive wheels of a bevel gear. Furthermore the invention relates to a wind turbine having such a mechanism.
In another aspect, the present invention relates to a method of stopping the complete rotation of the main shaft of a wind turbine comprising a motor to rotate a drive pinion of a bevel gear via a drive wheel of the said bevel gear, the said drive pinion being meant to turn at least one blade of the wind turbine around its longitudinal axis. The invention also relates to a mechanism for stopping the complete turning of a main shaft of a wind turbine comprising a motor to rotate a drive pinion in a bevel gear via a drive wheel, the said bevel gear being meant to pitch at least one blade around a longitudinal axis. Furthermore the invention relates to a wind turbine provided with such a mechanism.
DE 42 21 783 describes a device for setting the pitch angle of wind turbine blades. The device comprises an electrical motor mounted inside a fixed bearing. Surrounding the fixed bearing a longitudinal axis of rotation has been installed. On the rotational shaft blades have been installed which can be set at an angle relative to the main shaft and relative to a wind direction parallel to the longitudinal main shaft. The motor adjusts the pitch of the blades through a bevel gear. The longitudinal main shaft rotating and the pitch of the blades being correct, the motor must rotate at the same speed of rotation as the main shaft to maintain the correct pitch of the blades.
This is a major disadvantage. First, it requires very accurate control of the dynamic relations between motor and main shaft, i.e. the rotational speed of the motor in relation to the rotational speed of the main shaft. Second, the motor has to operate continuously to maintain the correct blade pitch. This results in extensive wear of the motor and entails large energy consumption for operating the motor. Furthermore it is necessary to control the speed of rotation variably and continuously relative to the variations in the speed of rotation of the main shaft, and the motor control risks being constantly somewhat behind compared with the main shaft, and consequently an optimal pitch angle of the blades cannot always be obtained.
Furthermore, the device is not capable of stopping or limiting the rotation of the main shaft in a controlled manner in case the motor cannot rotate because of e.g. current failure of the motor shaft rotation. The main shaft will, however, stop rotating after a while, since the blades once the motor no longer rotates synchroneously with the main shaft will soon be pitched at angular positions which are not optimal for the main shaft rotation. The blades will then reach a stable pitch characterized by the main shaft not rotating at the said pitch.
EP 0.094.106 describes a pitch controlling device according to the above. Thus, the device has a pitch motor for controlling the pitch of the blades in an operational situation of the wind turbine. A synchronizing shaft is connected to the blades through a bevel gear and the synchronizing shaft may be rotated by the pitch motor. In order for the pitch motor to rotate the synchronizing shaft, an electromagnetic clutch must be activated because the synchronizing shaft is journalled by means of bearings in the rotatable main shaft of the blades and the pitch motor is fastened to a stationary part of the wind turbine in relation to the main shaft.
However, the need for a clutch or other means of coupling the pitch motor and the synchronizing shaft by means of a disengagable coupling means is a disadvantage. The clutch may be worn or may even failure, which makes it impossible to control the pitch of the blades. If the pitch of the blades cannot be controlled then the wind turbine is not able to produce the maximum amount of effect or may even not be able to produce effect at all. If the clutch is worn or has a failure, then it is furthermore necessary to stop the wind turbine and to repair the clutch or exchange the clutch with a new one. This is time consuming which decreases the overall efficiency of the wind turbine. Furthermore it involves costs of a technician and the costs of spare parts. Lastly using a clutch or other disengagable coupling means may delay controlling of the pitch of the blades when as example a clutch has to be activated before controlling of the pitch of the blades can take place. Accordingly, the use of a clutch involves many disadvantages.
DE 196 34 059 and other prior art wind turbines achieve stopping the rotation of the main shaft by pitching the blades by means of individual motors at each blade. Pitching the blades in this way may have the same technical effect as the above-mentioned procedure and the main shaft stops so that the main shaft either effects no rotation at all or only rotates very slowly in its positive direction of rotation. However, this prior art necessitates the use of a pitch motor for each of the blades. Furthermore, an individual control of the pitch motors as well as a mutual control of the pitch motors will be necessary in order to assure that each blade of the wind turbine is having the same pitch as the other blades.
The object of the present invention is to provide a mechanism which does not suffer from the above mentioned disadvantages, and which will thus to a larger extent be able to establish and maintain the correct pitch of the blades, whether the control is sufficiently precise or not, and without major wear to the gear motor and the pitch motor, or high energy consumption for operating the pitch motor and without the risk of being the method and the mechanism being delimited in the controlling of the pitch because of sudden failure or ordinary wear of coupling means between the pitch altering means and the pitch motor.
The present object is in one embodiment of the invention achieved by a method characterised by the rotation of a drive wheel relative to the main shaft being brought to a standstill once the blades have reached the correct pitch, said drive wheel establishing a permanent coupling between the pitch motor and the synchronizing shaft.
Bringing the rotation of the pitch motor to a standstill relative to the main shaft while the said main shaft is rotating under normal operational conditions provides several advantages. Firstly, the wear of the pitch motor will be substantially reduced compared with a method continuing the rotation of the pitch motor rotation shaft also under normal operational conditions when correct pitch of the blades has been established.
Furthermore, continuously monitoring the speed of rotation of the pitch motor relative to the speed of rotation of the main shaft is no longer necessary. Finally, the pitch motor is used exclusively for controlling the pitch of the blades and is not used simultaneously for maintaining a speed of rotation of the drive wheel relative to the speed of rotation of the main shaft, a function which entails further technical control difficulties.
A mechanism for use in the method is characterised in that the motor is mounted on the longitudinal main shaft.
Mounting the motor on the main shaft provides the possibility of no longer having to exert control over the relative speed of rotation of the motor and the rotational shaft. The motor does not rotate if the correct pitch of the blades has been established. Any less exact tolerances and any wear to the mechanical parts will have no essential influence on maintaining the correct pitch of the blades, the motor controlling the pitch respective to given values such as the speed of rotation of the main shaft, the wind speed, etc, and the load on the mechanical parts will be purely static once the correct pitch has been established, since there are no dynamic relations between the motor, the main shaft and the bevel gear once the correct pitch of the blades has been established. Furthermore, there is no need for any disengagable coupling between the drive axle of the pitch motor and the synchronizing shaft. This also ensures that no mechanical wear or even mechanical failure occurs which may impede the controlling of the pitch of the blades and reduce the overall efficiency of the wind turbine.
In a preferred embodiment the mechanism is characterised by the synchronizing shaft being provided with a rotating portion of a brake, a fixed portion of the brake being mounted on the main shaft, and the brake being directed to maintain the synchronizing shaft relative to the main shaft in a situation when it is desirable that the pitch of the blades is maintained in a normal operational position.
Mounting a brake further provides the advantage that static relations between motor, main shaft, bevel gear and blades are not to be maintained by the motor operating as a brake to maintain static relations, these relations between main shaft, bevel gear and blades being instead maintained by a brake to relieve the motor when the correct pitch of the blades has been established and the motor therefore is not operating.
In a further aspect of the present invention, the purpose of the present invention is to bring the main shaft to a standstill in connection with a novel mechanism for regulating the pitch of the blades in normal operation.
This purpose is achieved by a method characterised by a synchronizing shaft for the drive wheel being slowed down synchronously with the rotation of the main shaft, and by the continued rotation of the main shaft turning the at least one blade of the main shaft at a pitch corresponding to a so-called pitch angle differing from an operationally optional pitch angle.
A preferred embodiment of the invention is characterised by the blades being permitted to turn in a positive and negative direction when the drive wheel synchronizing shaft is stopped, allowing the main shaft to rotate alternately in a forward and a reverse direction of rotation.
Bringing the rotation of the main shaft to a standstill is a novel feature, partly by the mechanism controlling the pitch of the blades being new, and partly by the main shaft coming automatically to a standstill in case of current failure of the motor controlling the blade pitch, the so-called pitch motor. Stopping takes place in such a way that the main shaft is not brought to a complete halt, but allowed to rotate around a point of equilibrium. This method of the invention allows the main shaft to rotate alternately and partly in a forward and partly in a reverse direction of rotation. This means that the main shaft bearings and the rotation collar bearings are in motion and therefore will not fail because of any unilateral static load nor because of any dynamic spot load when the main shaft and the rotation collars are completely stopped, nor will they be insufficiently greased by the slow turning of the main shaft in a positive direction of rotation only.
A mechanism to be employed by the method is characterised by a synchronizing shaft for the drive wheel being provided with a movable portion of a brake, a fixed portion of a brake being mounted a fixed frame relative to the main shaft, and by the brake being meant to secure the drive wheel synchronizing shaft relative to the fixed frame in case it is desirable that the pitch of the blades should be placed in a position for stopping the complete rotations of the main shaft.
By mounting a brake as defined the rotation of the main shaft can be slowed down in any case of pitch motor failure resulting from a current failure putting the pitch motor out of use. The negative brake will mainly be activated mechanically so that its function is independent of current.
The problems discussed above has been solved by means of the present invention which provides a device for controlling the pitch angle of a wind turbine blade of a wind turbine having
a main shaft rotatably connected to a base part of the wind turbine, and at least one blade connected to the main shaft, the connection enables rotation of the blade about a longitudinal axis of the blade,
pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade, and said the pitch altering means comprising a bevel gear with a drive wheel being rotated by the synchronizing shaft and drive pinions for turning the at least one blade at an angle
a synchronizing shaft connecting the driving means with the pitch angle altering means, at least a part of the synchronizing shaft being aligned with and extends along or parallel with a central axis of the rotatably connected main shaft, so that upon activation of the driving means a difference in angular rotation between the synchronizing shaft and the rotatably connected main shaft is introduced, as the pitch angle altering means is/are adapted to convert the angular rotation difference into a rotation of the at least one blade along its longitudinal axis, whereby the pitch angle of the at least one blade is/are altered by activating the driving means,
said pitch controlling device furthermore comprisingxe2x80x94an activatable driving means retained to the rotatably connected main shaft.
The activatable driving means is the part of the device according to the invention being activated when the pitch of the wind turbine is to be altered. As indicated, the activatable driving means is only to be activated when the pitch is to be altered, due to the fact, as will become clear from the description below and the accompanying examples of embodiments of the invention, that when the driving means is retained in a motion following the motion of the main shaft, no activation is needed in order to keep the pitch of the blades.
In fact, the synchronizing shaft rotates along with the main shaft as long a the pitch angle is not to be altered and therefore if a reference is chosen being the system rotating with the same angular rotation as the main shaft the observer following this reference system will observe the synchronizing shaft standing still. The difference in angular rotation should therefor in this connection be seen from point of reference fixed to the ground or the base of the wind turbine which is equivalent with the fact that an observer observing the motion of the synchronizing shaft will observe the synchronizing shaft rotating when the stated difference in angular rotation is present.
In preferred embodiment of the present invention the pitch controlling device may further comprise preventing means for preventing the pitch altering means from converting the angular rotation difference into a rotation of one or more of the at least one blade when the torque needed to rotate the one or more blade(s) along its longitudinal axis exceed a predetermined torque. Thisxe2x80x94or thesexe2x80x94preventing means is typically applied in order to assure that once a pitch setting of the blades has been provided then for instance the aerodynamic forces acting on the blades will not be able to alter the pitch. The preventing means may be applied by for instance disk brakes, pneumatic means or the like influencing directly or indirectly on the blades possible of being able to rotate along an axis extending substantially in the direction of the blades.
Furthermore, these preventing means may also serve a safety purpose. In this case the preventing means may prevent the blades from being turned when a difference in rotation is introduced between the main shaft and the synchronizing shaft, and a preventing means may be applied to each blade. Such a utility may be very important for instance when risk of blocking the turning of the blades for instance by ice or other deposits is present. In a preferred embodiment of the invention the present invention when serving a safety purpose, the preventing means is constituted by a friction clutch.
The activatable driving means may preferably be a motor, such as an electrical motor, a hydraulic driven motor or a pneumatic driven motor and the pitch altering means is preferably comprised of an bevel gear with a drive wheel being rotated by the synchronizing shaft and drive pinions for turning the at least one blade at an angle.
In a preferred embodiment of the pitch controlling device according to the present invention, the activatable driving means is/are located at a rear part of the main shaft and the pitch altering means is being located at a front end of the main shaft of the wind turbine. In order to connect these to part (means) the synchronizing shaft of which there may be more than one extends from the rear to the front end of the main shaft and even though it may be advantageous to let the synchronizing shaft(s) extend at the exterior of the wind turbines main shaft it is presently preferred that the synchronizing shaft(s) extends through the interior of the main shaft so that the two shafts in question is concentric.
In an embodiment where more than one synchronizing shaft is utilised each of these shafts may be connected to a blade so that each blade is pitched by one shaft. Also in this embodiment the shafts may advantageously extend through the interior of the wind turbines main shaft.
In another and presently most preferred embodiment of the present invention both the activatable driving means and the pitch altering means are located at a front part of the main shaft. Also in this embodiment the synchronizing shaft(s) may extend from the rear to the front end of the main shaft and the synchronizing shaft(s) extends through the interior of the main shaft.
To provide the pitch controlling device according to the present invention being able to lock the rotation of the synchronizing shaft to the rotation of the main shaft the synchronizing shaft(s) is/are provided with a part of a brake being able to rotate and a part of the brake being unable to rotate is mounted on the main shaft. This brake is preferably a positive brakexe2x80x94i.e. a brake providing a braking force only when activatedxe2x80x94whereby the pitch of the blades may be locked only intentionally in the sense that the brake in normal operation needs to be activated in order to lock the rotation of the synchronizing shaft to the main shaft.
A preferred brake applied in the above mentioned embodiment of the present invention is a brake wherein the part being able to rotate is a brake disc and the part of the brake being unable to rotate is a brake calliper having a brake shoe or alternatively wherein the part of the brake being able to rotate is a brake calliper having a brake shoe mounted on the synchronizing shaft and the part of the brake being unable to rotate is a brake ring mounted on the main shaft.
In another aspect it is desirable to be able to fixxe2x80x94or limitxe2x80x94the rotation of the main shaft when the wind turbine has been stopped. This is achieved as the synchronizing shaft(s) may be provided with a part of a brake being able to rotate and a part of the brake being unable to rotate is mounted on a stationary part of the wind turbine such as on the chassis.
Preferably different types of brakes are used in the embodiments of the present invention and in general when a fail safe brake is to be applied braking force is released by means of electric, hydraulic, mechanic or any other kind of applied dynamic force and when a controlling brake is to be applied braking force is applied by means of springs, hydraulic oil pressure or similar mechanically applied static force.
Power has to be supplied to the activatable driving means and in case this means is an electrical motor, electrical current to the electrical motor is preferably supplied by at least one slipring mounted concentrically with the main shaft and connected to a power supply. The same methodology may also be applied in case a pneumatic driven motor constitutes the activatable driving means and in this case the slipring will be designed to transfer fluids instead of electrical current.
In another preferred embodiment of the pitch controlling device according to the present invention the electrical current to the activatable driving means is preferably supplied by a power source contained in the main shaft or the main shaft being a part of the a power source. This power source may be a battery being charged for instance by induction. The use of a battery is especially useful when only fewxe2x80x94and perhaps smallxe2x80x94variations of the blades pitch is introduced since the activatable driving means only consumes power when activated and then there is time available for recharging the battery.
In still a preferred embodiment of pitch controlling device according to the present invention the wind turbine comprises a multi-pole generator having a rotor constituting the main shaft of the wind turbine.
In an embodiment of the invention where the wind turbine is being equipped with a multipole the generator is preferably being connected aligned with at the rear end of the wind turbine.
In another aspect the present invention relates to a method for controlling the pitch angle of a wind turbine using the pitch controlling device according to present invention where the synchronizing shaft and the activatable driving means are permanently connected. In the method aspect the pitch angle is controlled by:
activating the driving means and thereby instantly rotating the synchronizing shaft
when activating the driving means introducing a difference in angular rotation between the synchronizing shaft(s) and the main shaft,
transferring the difference in angular rotation between the synchronizing shaft and the main shaft to the pitch angle altering means,
de-activating the driving means and thereby instantly stopping the rotation of the synchronizing shaft
Even though the step as described above may be viewed upon as succeeding steps this is normally not the case as these steps are executed in a mechanical device wherein no or at least very little delay is aimed at. The sequence of steps rather expressed the way the altering of the pitch is initiated and the way the xe2x80x9cinformationxe2x80x9d is passed on to the blades. Also, xe2x80x9ctransferringxe2x80x9d may be viewed upon as the action of the bevel gear, for instance, when being active i.e. the teeth of the gear move relative to each other on the effect of the difference in rotation between the synchronizing shaft and the main shaft.
Actually, the alteration of the pitch angle is determined by the operation of the activatable driving means as this means is the one effecting the difference in rotation between the synchronizing shaft and the main shaft. The xe2x80x9cpredetermined amountxe2x80x9d may suitable be expressed in terms of radians and the like and as the gearing for instance in the gear transferring is knownxe2x80x94if such a gear is used as pitch altering meansxe2x80x94the difference in rotation and rotation of the blades also is known which may be expressed as a transferring function giving a functional relationship between for instance the turning of the blade per revolution of the driving means (in case a motor is used), whereby it is an easy task to determine the number of revolutions the driving means has to perform in order to turn the blade a predetermined amount.
After the pitch angle of the blades has been set the method according to the present invention may further comprise the step of retaining the angular position of the synchronizing shaft relative to the angular position of the main shaft, in order to assure that no further turning of the blade will accomplished. If this step is included in the method, the pitch altering process must be initiated by releasing the synchronizing shaft relative to the main shaft otherwise a difference in angular rotation between the two shafts may not be accomplished.
During normal operation of the wind turbine, i.e. when the turbine is being operated in production mode, and in particular the during normal application of the method for controlling the pitch angle, the pitch angle is controlled so that the pitching of the blades is between +2xc2x0 to xe2x88x9210xc2x0, primarily between +1xc2x0 to xe2x88x925xc2x0.
In yet another aspect the present invention relates to a method for stopping the rotation of the blades of a wind turbine. The method applies the method of controlling the pitch angle of wind turbine blade according to the present invention and the stopping is provided by retaining the synchronizing shaft to a stationary part of the wind turbine.
In order to for instance motioning the bearing in which the main shaft is sitting the main shaft is allowed to turn in either positive or negative direction when the synchronizing shaft is being retained to a stationary part of the wind turbine.
Typical and preferred values of the angle which the main shaft is allowed to turn in either positive or negative direction when the synchronizing shaft is being retained to a stationary part of the wind turbine is given by pitching the blades between 0xc2x0 to xe2x88x9220xc2x0 primarily xe2x88x9210xc2x0 to xe2x88x9215xc2x0, when the wind turbine is operating in a so-called negative stall mode.
When the wind turbine is operating in a so-called positive pitch mode the angle the main shaft is allowed to turn in either positive or negative direction when the synchronizing shaft is being stopped is given by pitching the blades around xe2x88x921xc2x0 to +90xc2x0, such as between 0xc2x0 to 65xc2x0 primarily 0xc2x0 to 40xc2x0.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.